Mesoscale Convective Systems in the Western Mediterranean Rigo, T.(1), and M. Berenguer (2)

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1 Mesoscale Convective Systems in the Western Mediterranean Rigo, T.(1), and M. Berenguer (2) (1) Servei Meteorologic de Catalunya, Barcelona (2) Centre of Applied Research in Hydrometeorology, Universitat Politècnica de Catalunya, BarcelonaTech

2 Presentation Index - Starting point - Why is important to understand MCS behavior? - Methodology - Results - Conclussions 2

3 Starting point Preliminary analysis using single C-band weather radar Main conclusions: TS (39%), LS (18%), and NS (43%). MCS clusters (CLU) constituted 51%. Mean area of 25,000 km2, Zmax ~ 47 dbz, echotop ~ 12 km Maximum frequency at 12 UTC and early afternoon Displacement towards E-NE 3

000 km 2 Set used Discrete (57 cases) (1996-2000) 5 y Continuous (2012-2016) 5 y Corrections Doppler Advanced (EHIMI)

4 Starting point VERSION AEMET (Old) SMC (Current) Time resolution 10 6 Spatial res. 2x2 km 2 1x1 km 2 Total area (coverage) km km 2 Set used Discrete (57 cases) ( ) 5 y Continuous ( ) 5 y Corrections Doppler Advanced (EHIMI) Main differences: - Change on the spatial coverage (increasing) - Change in the spatial and time resolutions (improving) - Change in the reflectivity corrections (higher quality) - Only few cases vs. a whole period of analysis 4

5 Starting point Why is important to understand MCS behavior? MCS are the most convective precipitation structures associated with floods that affect regions at mid-latitudes (e.g. Doswell et al., 1996; Gray and Marshall, 1998; Schiesser et al., 1995). MCSs are an important link between atmospheric convection and the larger-scale atmospheric circulation (Houze 2004). MCS behave as long-lived (>3 h), Parker and Johnson (2000) The organization of MCSs is also important for hazardous weather forecasting and warning (Parker and Johnson 2000). Commonly produce severe weather (Parker and Johnson 2004) Electrical behavior depends on the type (Parker et al 2000) Precipitation Efficiency in MCS is controlled by certain environmental factors (Market and Allen, 2003). 5

6 Starting point Why is important to understand MCS behavior? One of the convective modes better organized 6

7 Methodology Identification ~ 438,000 imagery were analyzed MCS were identified considering those regions with Z>12 dbz and A>10,000 km 2 (maybe very restrictive) => 40,082 imagery with a possible MCS (not all have been confirmed, ~11,000 were discarded because low reliability of shape) Stratiform/convective rainfall types have been discriminated considering 35 dbz threshold For each time that a MCS was identified, some features were calculated: date, centroid, total area, Zmax, Zmean, % of convective precipitation 7

8 Methodology Tracking Each MCS structure identified at one image has been tracked on time, considering distances between centroids of two consecutive cases of less than 35 km This criteria can produce some interruptions of life cycles, mainly in cases of merging and/or splitting Finally, 342 MCS were identified for the period of study ( ) 8

9 Methodology Tracking: example of MCS 9

10 Results Identification: Hour of the day There is a clear increase of number of observations from 12 UTC, with a maximum at 19 UTC 10

11 Results Tracking: Duration Most of MCS lasted for times between 4 and 8 hours (~55%) However, a significant number of cases with duration over 15 hours exists (~11%) Mean duration was 8.5 hours Probably, MCS lasted for more time (problem of coverage) in some cases 11

Results Tracking: Other parameters of interest (Quantiles) Parameter Q10 Q25 Q50 Q75 Q90 MEAN(Area) 15,300 18,300 22,600 28,600 40,800 MAX(Area) 21,300 25,700

12 Results Tracking: Other parameters of interest (Quantiles) Parameter Q10 Q25 Q50 Q75 Q90 MEAN(Area) 15,300 18,300 22,600 28,600 40,800 MAX(Area) 21,300 25,700 32,600 46,200 65,600 MAX(Zmax) TOTAL (Dist) Duration (h) Area: km 2 Zmax: dbz Dist: km 12

13 Results Identification: month of the year There are two periods of the year with a higher MCS observation, between cold and warm seasons CO-WA WA-CO CO-WA (March/April), ~26.5% of cases WA-CO (September-November), ~27.4% of cases SST and land surface reach similar values 13

14 Results MCS evolution (life cycle): beginning CO-WA WA-CO dbz dbz 14

15 Results MCS evolution (life cycle): pre-maturity CO-WA WA-CO dbz dbz 15

16 Results MCS evolution (life cycle): maturity CO-WA WA-CO dbz dbz 16

17 Results MCS evolution (life cycle): dissipation CO-WA WA-CO dbz dbz 17

Results Comparison between CO-WA and WA-CO seasons Area: km 2 Zmax: dbz Dist: km Parameter Q10 Q25 Q50 Q75 Q90 MEAN(Area) 15865.6 17764.3 22880.2 28351.4 43334.7 MAX(Area) 20758.4 26420.7 32517.

18 Results Comparison between CO-WA and WA-CO seasons Area: km 2 Zmax: dbz Dist: km Parameter Q10 Q25 Q50 Q75 Q90 MEAN(Area) MAX(Area) MAX(Zmax) TOTAL (Dist) Duration (h) MEAN(Area) MAX(Area) MAX(Zmax) TOTAL (Dist) Duration (h)

19 Results Comparison between CO-WA and WA-CO seasons Similarity in the life cycles in both cases Predominance of W to E in CO-WA and from SSW to NNE in WA-CO Practically all parameters (Z max, Area max, distance and duration) register larger values for MCS detected during the WA-CO season (this is coherent with the major number cases of floods during this phase of the year) Only Area mean shows higher values for CO-WA season, this is during this period MCS maintain the area for larger time intervals But... What happens with precipitation regimes? 19

20 Results Precipitation regimes The percentage of convective precipitation has a mean value of 25% in general for the whole set of MCS However, this value decreases in the case of CO-WA MCSs, not reaching the 20% On the contrary, the value is near 27% for the WA-CO MCSs MCS set Q10 Q25 Q50 Q75 Q90 ALL CO-WA WA-CO This means that MCSs in the WA- CO present larger convective precipitating areas 20

21 Results Precipitation regimes and electrical activity The previous behavior strongly agrees with the relationship between TL and cumulated precipitation associated to MCS While the total QPE reaches similar values for both types of seasons, the TL acquires larger values during the WA-CO season In this sense, the mean values of the rate NTL/QPE are 57.7 flashes/mm (CO-WA) and flashes/mm (WA-CO) 21

22 Conclusions Mesoscale Convective Systems in the Western Mediterranean The continuous database of radar imagery for the period have been analyzed in order of identifying and tracking MCS => 342 cases have found Two main periods with maxima of MCS observation, coinciding with the transition between Cold and Warm seasons (and vice versa) Although the structure of MCS on both periods is similar, we have found important differences, on respect the area, distance, duration or intensity Moreover, autumn events (WA-CO) cases shown higher percentages of convective precipitation, as more number of total lightning 22

23 gencat.cat

24 Methodology Areas with each type of precipitation (normalized on respect the max) STRATIFORM CONVECTIVE 24

25 Methodology Tracking: example of MCS that last for more than 24 h Gap between centroids 25

Mesoscale Convective Systems in the Western Mediterranean Rigo, T.(1), and M. Berenguer (2)

Mesoscale Convective Systems in the Western Mediterranean Rigo, T.(1), and M. Berenguer (2) (1) Servei Meteorologic de Catalunya, Barcelona (2) Centre of Applied Research in Hydrometeorology, Universitat